Toughening of polymers by graphene

Graphene has been regarded as the next-generation carbon nanofiller for polymer nanocomposites. Owing to its superior physical properties, it produces a dramatic improvement in properties of polymers at very low filler loadings. In the past few years, toughening of polymers by graphene has been studied intensively. This article reviews the typical preparation methods of graphene and graphene/polymer nanocomposites. The authors summarize the enhancement effect, optimal filler loading and toughening mechanism for the polymer composites. Effects of some important factors including graphene content, thickness, sheet size, state and interfacial bonding with polymer chains have been addressed. Accordingly, the current challenges and future perspectives for the toughening of polymers by graphene are indicated

An investigation of the mechanism of graphene toughening epoxy

The three different sized chemical functionalized graphene (GO) sheets, namely GO-1 (D50 = 10.79 μm), GO-2 (D50 = 1.72 μm) and GO-3 (D50 = 0.70 μm), were used to fabricate a series of epoxy/GO nanocomposites. Fracture toughness of these materials was assessed. The results indicate that GO sheets were dramatically effective for improving the fracture toughness of the epoxy at a very significant low loading. The enhancement of the epoxy toughness was strongly dependent on the size of GO sheets incorporated. GO-3 with smaller sheet size gave the maximum reinforcement effect compared with GO-1 and GO-2. The incorporation of only 0.1 wt% GO-3 was observed to increase the fracture toughness of pristine epoxy by ∼75%. The toughening mechanism was well understood by fractography analysis of the tested samples. Massive cracks in the fracture surfaces of the epoxy/GO nanocomposites were observed. The GO sheets effectively disturbed and deflected the crack propagation due to its two dimensional structure. GO-3 sheets with smaller size were highly effective in resisting crack propagation, and a large area of whitening zone was observed. The incorporation of GO also enhanced the stiffness and thermal stability of the epoxy

Effect of graphene oxide sheet size on the curing kinetics and thermal stability of epoxy resins

This work revealed the influences of graphene oxide (GO) sheet size on the curing kinetics and thermal stability of epoxy resins. A series of GO/epoxy nanocomposites were prepared by the incorporation of three different sized GOsheets, namely GO-1, GO-2 and GO-3, the average size of which was 10.79 μgm, 1.72 μgmand 0.70 μgm, respectively. The morphologies of the nanocomposites were observed by field emission gun scanning electron microscope. The dispersion quality of each sized GO was comparable in the epoxy matrix. The curing kinetics was investigated by means of differential scanning calorimetry and analyzed based on kinetics model. Addition of a small amount of GO (0.1 wt%) exhibited strong catalytic effect on the curing reaction of epoxy resin. The activation energy was reduced by 18.9%, 28.8% and 14.6% with addition of GO-1, GO-2 and GO-3, respectively. GO-2 with medium size (1.72 μgm) showed the most effective catalysis on the cure. The thermal stability of the cured resins was evaluated based on thermogravimetric analysis. GO/epoxy nanocomposites showed improved thermal stability in the range of 420 °C-500 °C, compared with the pure resin. A∼4%more residue was obtained in each of the incorporated system. The variations of GOsheet size did not influence the enhancement effect on the thermal stability

A comparative study on the effect of carbon fillers on electrical and thermal conductivity of a cyanate ester resin

Carbon fillers including multi-walled carbon nanotubes (MWCNTs), carbon black (CB) and graphite were introduced in a cyanate ester (CE) resin, respectively. The effects of the fillers on the electrical and thermal conductivity of the resin were measured and analyzed based on the microscopic observations. MWCNTs, CB and graphite exhibited percolation threshold at 0.1 wt%, 0.5 wt% and 10 wt%, respectively. The maximal electrical conductivity of the composites was 1.08 S/cm, 9.94 × 10−3 S/cm and 1.70 × 10−5 S/cm. MWCNTs showed the best enhancement on the electrical conductivity. The thermal behavior of the composites was analyzed by calorimetry method. Incorporation of MWCNTs, CB and graphite increased the thermal conductivity of CE resin by 90%, 15% and 92%, respectively. Theoretical models were introduced to correlate the thermal conductivity of the CE/MWCNTs composite. The interfacial thermal resistance between CE resin and MWCNTs was 8 × 10−8 m2K/W and the straightness ratio was 0.2. The MWCNTs were seriously entangled and agglomerated. Simulation results revealed that thermal conductivity of the CE/MWCNTs composites can be substantially elevated by increasing the straightness ratio and/or filler content of MWCNTs

A two weight local Tb theorem for the Hilbert transform

We obtain a two weight local Tb theorem for any elliptic and gradient elliptic fractional singular integral operator T on the real line, and any pair of locally finite positive Borel measures on the line. This includes the Hilbert transform and in a sense improves on the T1 theorem by the authors and M. Lacey.Comment: 121 pages, 3 figures, 50 pages of appendices. We correct three gaps in the treatment of the stopping form in v12: the proof of Lemma 9.3 there requires a larger size functional, a collection of pairs is missing from the decomposition at the bottom of page 149, and an error was made in the definition of restricted norm of a stopping form. Main results unchange

Study of Heavy Flavor Dynamics and Energy Loss using b jet Shapes Measured with CMS

Quantum Chromodynamics (QCD), the theory describing strong interactions, have achieved remarkable success in describing many aspects of experimental data from particle physics experiments, especially in perturbative regime. However, the higher-order contributions and non-perturbative effects in particle production present remaining challenges for the theory. These contributions are essential for modeling the production and subsequent fragmentation of b quarks; experimental inputs on the subject are essential for further theoretical developments. Experimental studies of jets initiated by the heavy b quarks (known as "b jets") provide an excellent opportunity to improve our understanding of QCD. The details of b-jet fragmentation in the vacuum and modification of b-jet shower properties due to interactions with quark-gluon plasms (QGP) are novel aspects of this work. This study presents the first measurements of b jet shapes representing the transverse momentum distribution of jet constituents about the jet axis, measured in proton-proton (pp) and lead-lead (PbPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV using the data collected by the CMS detector.Measured b-jet distributions are compared to inclusive jets, elucidating fragmentation differences between the light and the heavy flavor partons. A deficit of transverse momenta at small radial distances from the jet axis is observed in charged jet constituents distributions around b jets relative to inclusive jets. Model predictions for pp data provided by the PYTHIA and HERWIG++ event generators indicate that the gluon splitting contribution plays an important role in b quark production. A comparison of b jet shapes between pp and PbPb collisions shows this depletion is not substantially affected by the presence of QGP. On the other hand, this comparison indicates that the energy flow around the b jet axis is redistributed towards larger radii when QGP presents. This effect is more pronounced for b jets

Effects of carbon-based nanofillers on the performance of cyanate ester and epoxy resins

Effects of carbon-based nanofillers on the performance of cyanate ester and epoxy resin

Generalized Scalar-on-Image Regression Models via Total Variation

<p>The use of imaging markers to predict clinical outcomes can have a great impact in public health. The aim of this article is to develop a class of generalized scalar-on-image regression models via total variation (GSIRM-TV), in the sense of generalized linear models, for scalar response and imaging predictor with the presence of scalar covariates. A key novelty of GSIRM-TV is that it is assumed that the slope function (or image) of GSIRM-TV belongs to the space of bounded total variation to explicitly account for the piecewise smooth nature of most imaging data. We develop an efficient penalized total variation optimization to estimate the unknown slope function and other parameters. We also establish nonasymptotic error bounds on the excess risk. These bounds are explicitly specified in terms of sample size, image size, and image smoothness. Our simulations demonstrate a superior performance of GSIRM-TV against many existing approaches. We apply GSIRM-TV to the analysis of hippocampus data obtained from the Alzheimers Disease Neuroimaging Initiative (ADNI) dataset. Supplementary materials for this article are available online.</p

Additional file 2: Table S1. of XLF-mediated NHEJ activity in hepatocellular carcinoma therapy resistance

Alteration of NHEJ pathway genes in HCC by RNA-seq. (DOCX 56 kb

Mind Wandering in Chinese Daily Lives – An Experience Sampling Study

<div><p>Mind wandering has recently received extensive research because it reveals an important characteristic of our consciousness: conscious experience can arise internally and involuntarily. As the first attempt to examine mind wandering in a non-western population, the present study used experience-sampling method to collect the daily momentary mind wandering episodes in a Chinese sample. The results showed that mind wandering was also a ubiquitous experience among the Chinese population, and, instead of emerging out of nowhere, it was often elicited by external or internal cues. Furthermore, most of the mind wandering episodes involved prospective thinking and were closely related to one’s personal life. Finally, the frequency of mind wandering was influenced by some contextual factors. These results taken together suggest that mind wandering plays an important role in helping people to maintain a continuous feeling of “self” and to prepare them to cope with the upcoming events.</p> </div